Force ISO8601 date format for locale 'en'

src/pretix/helpers/formats/en/formats.py

@@ -0,0 +1,2 @@
+SHORT_DATE_FORMAT = 'Y-m-d'
+SHORT_DATETIME_FORMAT = 'Y-d-m P'

src/pretix/settings.py

@@ -232,6 +232,10 @@ LOCALE_PATHS = (
     os.path.join(os.path.dirname(__file__), 'locale'),
 )
 
+FORMAT_MODULE_PATH = [
+    'pretix.helpers.formats',
+]
+
 LANGUAGES = [
     ('en', _('English')),
     ('de', _('German')),